Gas dispersion apparatus for molten aluminum refining

ABSTRACT

The maximum useful rate of aluminum refining is increased by baffle means positioned across the refining chamber under the rotor of a spinning nozzle in the refining chamber, with open spaces to facilitate cleaning being provided in the vicinity of the side wall of the refining chamber.

This application is a continuation-in-part of U.S. application Ser. No.07/656,849, entitled IMPROVED GAS DISPERSION APPARATUS FOR MOLTENALUMINUM REFINING, filed Feb. 19, 1991, which issued as U.S. Pat. No.5,234,202, dated Aug. 10, 1993.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to the refining of molten aluminum. Moreparticularly, it relates to the dispersion of a gas in the moltenaluminum.

2. Description of the Prior Art

Molten aluminum, as derived from most common sources, such as primarymetal, scrap and re-melt ingot, usually must be purified before beingcast into ingots, sheets or bars. This may be done by bubbling an inertgas, i.e., nitrogen or argon, through the aluminum in molten form. Insome embodiments, a halogen gas, usually chlorine, is added, or thehalogen gas may be used alone for such purification purposes. This typeof treatment can remove dissolved hydrogen, alkali metals such as sodiumand lithium, and small solid particles such as aluminum oxide. Theeffectiveness of a given volume of gas in such treatment is increased byreducing the bubble size of the gas in the molten aluminum, therebyincreasing the total gas-metal surface area. The effectiveness of thegas bubbles is also increased by the dispersing of said gas bubblesthroughout the body of molten aluminum to be treated. One very effectiveway of both making small bubbles and dispersing them is by the use of aspinning nozzle positioned in the body of molten aluminum. Commercialsystems are available for this purpose, including the SNIF™ systems ofUnion Carbide Industrial Gases Inc. for in-line refining of metalsflowing from a holder to a casting station. The Pelton patent, U.S. Pat.No. 4,784,374, discloses and illustrates a particular embodiment of saidSNIF™ system.

The refining rate of such a spinning nozzle system can be increased byincreasing the process gas flow rate employed therein. It is usuallyalso necessary to increase the nozzle rotating speed to continue thedesired making of small bubbles and the dispersing of said small bubblesthroughout the molten aluminum in the refining zone of the system. Suchincrease in gas flow and nozzle rotating speed are usually accompaniedby increased turbulence on the surface of the molten aluminum. Themaximum refining rate of a given refining system, however, is limited bythe maximum surface turbulence or roughness that can be toleratedtherein.

Excessive surface turbulence is undesirable in a refining system forseveral reasons. Thus, the increased metal surface area that is producedthereby leads to higher reaction rates with any reactive gas that mightbe present. For example, oxygen from air will react to form aluminumoxide films, and water vapor from the air will react to form hydrogen inthe metal and oxide films. Furthermore, when solid particles are carriedto the molten metal surface by the refining gas bubbles, surfaceturbulence may interfere with their desired separation from the bubblesand their incorporation into the floating dross layer formed over thebody of molten aluminum. Excessive turbulence may also cause floatingdross to be re-dispersed into the molten aluminum. While the quantativeeffects of excessive surface turbulence are difficult to measure, thoseskilled in the aluminum refining art are nevertheless aware fromexperience that high surface turbulence is undesirable, and will striveto limit such surface turbulence to levels considered acceptable inpractical commercial operations.

There is a need and desire in the art to increase the aluminum refiningrate of spinning nozzle systems. Thus, it is desired to increase gasflow rates and nozzle rotating speeds so as to increase the maximumuseful rate of refining without the onset of excessive surfaceturbulence as presently encountered in such spinning nozzle systems.

It is an object of the invention, therefore, to provide an improvedrefining system for the production of aluminum.

It is another object of the invention to provide an aluminum refiningsystem employing one or more spinning nozzles and capable of operatingat enhanced refining rates.

It is a further object of the invention to provide a spinning nozzlealuminum refining system capable of operating at higher gas flow ratesand nozzle rotating speed without a corresponding increase in turbulenceon the surface of the molten metal.

With these and other objects in mind, the invention is hereinafterdescribed in detail, the novel features thereof being particularlypointed out in the appended claims.

SUMMARY OF THE INVENTION

The maximum useful refining capacity or rate of a spinning nozzle typealuminum refining system is increased by the incorporation of a verticlebaffle or rib across the bottom of the refining chamber and under thecenter of the rotor of the spinning nozzle device. The baffle isadvantageously provided with open spaces near the ends thereof tofacilitate draining and cleaning operations in the refining chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is hereinafter described with reference to theaccompanying drawings in which:

FIG. 1 is a plan view of a spinning nozzle 20 rotor as used in the SNIF™system referred to above;

FIG. 2 is a side elevational view of said spinning nozzle rotor and thestator commonly employed therewith;

FIG. 3 is a plan view of another type of 25 spinning nozzle employedwithout a stator;

FIG. 4 is a side elevational view of the spinning nozzle of FIG. 3;

FIG. 5 is a side elevational view of a typical spinning nozzle type ofmolten aluminum 30 in-line refining system, including the baffle meansemployed in the practice of the invention;

FIG. 6 is a plan view of the spinning nozzle system of FIG. 5;

FIG. 7 is a cross-sectional view of a particular embodiment of saidbaffle means used in the practice of the invention;

FIG. 8 is a side elevational view of a 5 particular embodiment of thespinning nozzle refining system of the invention incorporating aparticular baffle means configuration;

FIG. 9 is a side elevational view of a particular aluminum refiningchamber useful in the practice of the invention;

FIG. 10 is a plan view of the aluminum refining chamber of FIG. 9;

FIG. 11 is a plan view of a particularly desirable rotor for use in thepractice of the invention;

FIG. 12 is a side elevational view of the rotor FIG. 11 together with astator used in conjunction therewith in an embodiment of the invention;

FIG. 13 is a side elevational view of a embodiment of the inventionproviding for open spaces at the ends of baffle means used in thepractice of the invention; and

FIG. 14 is a side elevational view of another embodiment of theinvention providing for open spaces at the ends of baffle means used inthe practice of the invention.

DETAILED DESCRIPTION OF THE INVENTION

As spinning nozzle, for purposes of the invention, will be understood tocomprise a cylindrical rotor having protruding vanes and some means forintroducing a process gas into a space between the vanes. The rotor usedin the SNIF™ systems referred to above is shown in FIGS. 1 and 2 of thedrawing, with said rotor being represented by the numeral 1 and beingmounted on shaft 2 having drive means, not shown, for the rotation ofsaid rotor 1. The rotor is illustrated as having desirable vanes 3extending from the body thereof in a spaced apart configuration aroundthe circumference of said rotor 1. Slots existing between individualvanes 3 are denoted by the numeral 4. Said vaned rotor 1 is shown inFIG. 2 together with stator 5 positioned around shaft 2 above saidrotor. Process gas that is passed downward in the annular space betweenshaft 2 and stator 5 enters rotor 1 from a space 6 between the top ofrotor 1 and the bottom of stator 5.

In the embodiment shown in FIGS. 3 and 4, the spinning nozzle comprisesa rotor without an accompanying stator. In this embodiment, rotor 7 ismounted on shaft 8 and includes vanes 9 spaced apart around thecircumference thereof, with slots 10 existing between adjacent vanes 9.Shaft 8 has hole 11 extending therethrough so as to enable process gasto be passed downwardly therein to rotor 7. In order to introduce gas tothe space between the vanes, i.e., to slots 10, rotor 7 contains gasexit holes 12 therein that extend from hole 11 in shaft 8 outwardly tosaid slots 10 between vanes 9.

A typical spinning nozzle type of molten aluminum in-line refiningsystem is illustrated in FIG. 5 of the drawings, with a rotor-statorassembly such as is shown in FIGS. 1 and 2 being included forillustrative purposes only. In this system, an insulated, refractorylined refining chamber 13 is shown with an insulated cover 14 and withmolten aluminum inlet 15 and refined molten aluminum outlet 16positioned at opposite sides thereof. During operation, the moltenaluminum is maintained at a desired molten aluminum level 17 with thespinning nozzle assembly, generally represented by the numeral 18, beingpositioned in the molten aluminum below operating level 17 with stator19 and shaft 20 enclosed thereby extending upward through insulatedcover 14. Rotor 21 is positioned below said stator 19 so as to reducethe size of gas bubbles present in the space 22 between stator 19 androtor 21 and to disperse said gas bubbles throughout the body of moltenaluminum, which is denoted by the numeral 23, present in refiningchamber 13 during aluminum refining operations therein.

Molten aluminum continuously enters refining chamber 13 through inlet 15and is continuously refined by the action of spinning nozzle 18 as itmixes the body of molten aluminum 23 and disperses gas introducedtherein through said spinning nozzle in the form of small gas bubblesand distributes said small bubbles throughout the molten aluminum. Therefined molten aluminum is continuously passed from refining chamber 13through outlet 16. Dross resulting form the extraction of solidparticles and alkali metals form the molten aluminum floats on thesurface of the molten aluminum and is skimmed off thereof. Hydrogenremoved from the molten aluminum by the process gas bubbles enters thegas space 24 above molten aluminum operating level 17 and is removedfrom refining chamber 13 along with spent process gas.

In the practice of the invention, vertical baffle means 25 is positionedacross the bottom of the interior of refining chamber 13 under rotor 21to increase the maximum useful refining capacity of the spinning nozzlealuminum refining system. As shown in FIG. 6, baffle means 25 isadvantageously positioned under the center of rotor 21. Baffle means 25may be a simple rectangular sheet of refractory material, sufficientlythick to have adequate strength for its intended purpose. A convenientshape of said baffle means 14 in practical operating systems is shown inFIG. 7, whereby the roughly triangular cross-section is strong enough toresist mechanical damage during post-refining cleaning operations andalso provides slanting surfaces that make it easier to clean the bottomof refining chamber 13 than if baffle means had vertically extendingwalls as in the FIG. 5 embodiment.

In the FIG. 8 embodiment, baffle means 25 is shown as having a constantheight section 26 under the center and in the vicinity of rotor 21, withraised end sections 27 and 28 extending upward in the direction of theside walls of refining chamber 13. This increasing height baffle meanshas been found to provide a small increase in refining effectiveness,but it is not an essential feature of the invention.

The spinning nozzle used in aluminum refining is usually positioned atthe center of a rectangular refining chamber as shown in FIG. 6. Itshould be noted, however, that the spinning nozzle may be located offcenter in said refining chamber if convenient for some reason, such asconvenience of construction or access. In any event, the baffle means ofthe invention preferably will be positioned under the center of therotor element of the spinning nozzle. It should be noted that, if therefining chamber is rectangular with approximately vertical sides, saidbaffle means may be positioned parallel to either the short side, as inthe FIG. 6 embodiment, or the long side of the rectangle. However, it isgenerally most effective when positioned parallel to the short side.Refining chamber 13 may also have a slanging wall, such as wall 129 ofFIG. 9, at one end of refining chamber 13, or at one side thereof, tofacilitate cleaning or emptying of the chamber. In such embodiments,baffle means 25 is preferably positioned parallel to the base ofslanting wall 29.

The useful height of the baffle means of the invention will beunderstood to depend upon the operating circumstances pertaining to anyparticular refining application, e.g. the size of the refining chamberand of the spinning nozzle employed therein. Typical refining systemspresently in use have spinning nozzle ranging in size from about 7" to10" in diameter and about 21/2" to 4" in height. Typical refiningchambers are about 20" to 30" in width, about 30" to 40" in length, withmolten metal depths of about 25" to 35". For such size systems, theheight of the baffle means of the invention is typically about 2" to 8"or more, with the baffle means height preferably from about 3" to about5".

The distance between the top of the baffle means of the invention andthe bottom of the spinning nozzle rotor may be varied from a fraction ofan inch, e.g. on the order of about 1/2", up to about 4" or more. Itshould be noted that a very small clearance, e.g. 1/2" will work well inrelatively clean molten aluminum. In practice, however, small, hardpieces of refractory from up-stream sources may inadvertently be presentin the molten aluminum. Such pieces of refractory can become caughtbetween the baffle of the invention and the rotor, causing breakage ofthe rotor or its shaft, typically made of graphite. From a practicaloperating viewpoint, therefore, it is generally desirable to employ aclearance in the range of from about 2" to about 3" between the top ofthe baffle means and the bottom of the rotor. A clearance of about 2"over a baffle 4" high, for example, will avoid the likelihood of damagefrom most kinds and sizes of refractory pieces commonly found inoperating SNIF™ systems for the refining of aluminum.

The practice of the invention was illustrated in the following examplesbased on typical water model tests. For such purposes, full size modelsof the refining chamber and the spinning nozzle were employed. Water wascirculated through the model at a volumetric flow rate equivalent to thealuminum metal flow being evaluated. Oxygen is dissolved in the water bybubbling air therethrough in a separate chamber, and the dissolvedoxygen content of the incoming and outflowing water were measured. Theincoming water contained generally about 7 ppm of dissolved oxygen. Thespinning nozzle was operated with nitrogen as the process gas. Thenozzle operation in the water model simulation thus acted to stripoxygen out of the water in a manner corresponding to that by whichhydrogen is stripped out of molten aluminum in actual aluminum refiningoperations. The system performance is derived from measurements ofoxygen removal at various liquid flow rates, nozzle operatingparameters, i.e., gas flow, rotating speed and design, and overallrefining system design.

Since the process gas in an aluminum refining system is heated to atemperature of about 700° C. in actual operation, it expands to about 3times its original volume under ambient conditions. In order to providethe same volume of gas in the water employed in the water model tests asis used in the molten aluminum being refined in actual practice, the gasflow in the water model is set at 3 times the gas flow being modeled orsimulated. With respect to the examples below, reference is made hereinto the gas flow being simulated rather than to the three times volumeactually employed.

EXAMPLE NO. 1

A model was made of the refining system shown in FIGS. 9 and 10. Asshown in FIG. 10, the model simulates a two-nozzle system in whichrefining chamber 30 has a partition 31 therein that serves to separatethe operating space into two separate refining compartments, with moltenaluminum being passed into first compartment 32 through inlet 33 andwith refined molten aluminum being discharged from the system throughoutlet 34 from second compartment 35. Crossover hole 36 in partition 31enables molten aluminum to pass from first compartment 32 to secondcompartment 35. Spinning nozzle assembly 37 is positioned in saidcompartment 32, and a second spinning nozzle assembly 38 is positionedin said compartment 35.

Each compartment was 24" wide and 30" long at the bottom. Front wall 29of each compartment was slanted at an angle of 20° to facilitateemptying and cleaning. The liquid depth during operation was about 30".Nozzles 37 and 38 were centered in the 24" direction. Each said nozzlewas positioned about 2" from the back wall to provide reasonable accessfor cleaning from the front of the model. The rotor and stator used ineach compartment were of the type shown in FIGS. 1 and 2, with the outerdiameter of the rotor being 71/2", and the rotor height being 2 7/16".The rotor was formed with 8 vanes, each of which were 11/4" long and 1"wide. The bottom of the rotor was 41/2" above the bottom of the refiningchamber in each compartment. When such a system is operated in analuminum foundry, the maximum refining rate is usually set at 41/2 CFMof argon per nozzle, with the rotating speed of the nozzle being about500 RPM. Under these conditions, the metal surface is as turbulent asintolerable in most practical commercial operations. A much smoother andmuch more desirable surface condition is obtained by operating at only 3CFM of argon flow and 450 RPM nozzle speed. These conditions arefrequently used in customary practice even though the refining rate, asmeasured in water model tests is reduced to about 75% of the refiningrate for the maximum higher gas flow and nozzle speed indicated above.In water model testing simulating these two operating conditions, it wasfound that the resulting surface turbulence matched fairly well with theobserved turbulence encountered in actual refining system operations.

In accordance with the invention, baffle 39, which was 31/2" high by3/4" thick, was then placed under the center of the rotor of nozzles 37and 38 and parallel to slanting front wall 29 and to the back wall ofrefining chamber 30. When the thus modified system was operated at 610RPM and a simulated gas flow rate of 5 CFM, the surface was as good,i.e., free of undue turbulence, as it was without baffle 39, at 500 RPMand 41/2 CFM but the refining rate was advantageously increased by over50%. When the modified system was operated at a simulated rate of 450RPM and 3 CFM, the surface of the liquid was as desirably smooth as ithad been without incorporation of baffle 39 in the system and at said450 RPM and 3 CFM, but the refining rate was increased by about 35%.

EXAMPLE NO. 2

A rotor of the type shown in FIGS. 3 and 4 was placed at the center of arectangular refining chamber 24"×30" with all vertical walls. The liquiddepth during operation was maintained at about 30". Rotor 7 was 10" indiameter by 4" high, with 8 vanes about 1 1/4" long. Process gas wasinjected through holes 12 in the rotor between vanes 9 for exit intoslots 10 between said vanes. The bottom of rotor 7 was 3" above thebottom floor of the chamber. The maximum operating condition for arelatively smooth surface was at a simulated gas flow of 3 CFM and at200 RPM rotor speed. Under such conditions, there was occasionalundesirable upward eruptions from the liquid surface due to theundesired existence of large gas bubbles.

The nozzle was then raised 2" to provide a bottom clearance of 5", andthe baffle of the invention, 31/2" high by 3/4" thick, was placed underthe center of the rotor and oriented parallel to the shorter wall of thechamber. In this embodiment of the practice of the invention, the nozzlecould be operated at a simulated rate of 5 CFM gas flow and a speed of250 RPM with the surface of the liquid being as smooth as that obtainedat the lower maximum operating conditions of conventional practice. Infact, the liquid surface was even better in the practices of theinvention than previously in that there were none of the undesirableupward eruptions referred to above. Furthermore, the refining rate wasincreased by 70% in the practice of the invention.

In a preferred embodiment of the invention, even better refining rateswere obtained at a given surface roughness by the use of a special rotorin conjunction with the use of the baffle means of invention. This rotoris shown in plan view of FIG. 11 and in side view in conjunction with adesirable stator shape in FIG. 12. The essential difference between thespecial rotor and a conventional vaned rotor as shown in FIGS. 1 and 2is that the liquid entry from the bottom of the rotor is partiallyrestricted, while liquid entry from the top of the rotor is not sorestricted. The special rotor design also directs the flow of liquidfrom the bottom into the base of the rotor slots and in a mostly upwarddirection. In addition, this special rotor configuration presents acontinuous circular shape on its lower outer edge. This shape is muchless subject to damage from hard solid pieces of foreign material thatmay be drawn up and into the rotor during commercial operations.

The special rotor, represented by the numeral 40 and mounted on rotordrive shaft 41 in FIG. 11, has vanes 42 positioned around the rotorperiphery, with slots 43 located between adjacent vanes. As shown inFIG. 12 and unlike the rotor of FIGS. 1-4, slots 43 do not extend to thefull height of adjacent vanes 42 but for only a slot portion 44 thereof.Below said slot portion 44, restricted portion 45 remains and forms,together with adjacent vanes 42, a cylindrical base portion 46 of rotor40, as will be seen in FIG. 11. In order to provide for passage ofmolten aluminum from the region below the rotor to slot portion 44,openings or holes 47 are provided in each said restricted portion 45.Said openings 47 are preferably positioned essentially at the innermostend of restricted portion 45, and provide access for molten aluminum toslot portion 44 of each slot 43, preferably toward the innermost portionthereof for enhanced molten liquid flow effect.

In the use of the invention, it is desirable that the process gas enterthe rotor continuously and uniformly in all rotor slots 44. However, theturbulent motion of the liquid as it approaches the rotor from abovetends to produce a non-uniform gas flow to the rotor. If, for example,the liquid momentarily flow toward the rotor more rapidly from one sidethereof, it tends to shut off the gas exiting on that side and toincrease the flow to other parts of the rotor. This tendency can bereduced by making the gap 49 between the top of rotor 40 and the bottomof stator 48 very small so as to produce an appreciable pressure drop atthis point. For such purpose in practice, however, it is necessary toreduce this gap to about 0.020" or less for most embodiments. Since thegap is set during assembly of the rotor-stator unit at a desired plantlocation, the achieving of this very small gap is dependent upon thecare and skill with which it is assembled. In addition, the gap canchange in operation due to temperature changes and the like. A moresuitable means for achieving such gas flow control is thus desired forpractical commercial applications.

As shown in FIG. 12, a preferred means of achieving desired gas flowcontrol is obtained simply by the inclusion of a stator boss andcorresponding rotor recess. Thus, boss portion 50 is provided at thebottom end of stator 48 and is adapted to fit into a recess portion 51at the top of rotor 40. The small gap passage required to produce moreuniform gas distribution throughout the rotor is provided by radial gap52 between the outside diameter of boss 50 and the inside diameter ofrecess 51 on the side toward rotor slot 44. This gap 52 can becontrolled at the point of manufacture and is not dependent, as is aconventional small gap between the top of the rotor and the bottom ofthe stator, upon the care and skill of assembly of the rotor-statorunit. Small radial gap 52 will generally be controlled at about 0.025",although somewhat larger or smaller distances can be employed dependingupon the overall structure of the unit and of the refining chamber andapplication with which it is to be employed. In this preferredembodiment, stator boss portion 50 and rotor recess portions 51 can bothbe about 1/4" high or deep in common practice. The vertical gap 49between the bottom of stator 48 and the top of rotor 40 and between thebottom of stator boss portion 50 and the top of rotor recess portion 51,can be set at a greater tolerance, e.g., about 1/16" with the exactsetting not being critical for the desired gas flow control purposes. Asshown in the illustrated embodiment of FIG. 12, process gas passesdownward through gas entry passage 53 adjacent rotor shaft-statorbearing 54, and through gas passageway 55 to stator-rotor gap 49,including small radial gap 52 for the desired gas flow control. The gasexits from stator-rotor gap 49 and enters rotor slots 44 in a continuousand uniform manner. The stator diameter is preferably made slightlylarger than the root diameter of the rotor, i.e., the diameter at thebase of the vanes, so that the process or sparging gas is caused to passdownward into the rotor slots by the downward flow of molten aluminum,and none of said process gas is allowed to escape upward and avoid beingdispersed by the action of the rotor. When no stator is employed, theprocess gas is introduced into the rotor via holes that lead to thespaces between rotor vanes as shown in FIGS. 3 and 4. In the absence ofa stator, it may be desirable to employ a cylindrical abutment toessentially duplicate the function of the stator in directing the flowof process gas downward.

The area of the openings 47 in restricted portion 45 in the bottom ofthe rotor in relation to the total opening, if unrestricted, isgenerally in the range of from about 25% to about 75%, with an openingarea of about 50% being preferred. The height of restricted portion 45of rotor 40 should be generally in the range of from about 20% to about40% of the overall rotor height, with a restricted portion height ofabout 30% being preferred for use in typical sized refining chamberunits.

The rotor as shown in FIG. 11 has rounded corners at the base of thevanes, and the holes for molten aluminum entry from below the rotor alsohave rounded edges. While the radii thereof are not essential to theperformance of the rotor, they result from a convenient means ofmachining the rotor by cutting slots and entry holes therein with avertically oriented end mill.

EXAMPLE NO. 3

The system as described with respect to Example 1 was employed infurther tests using the baffle mean of the invention except that thespecial rotor configuration described above was employed, together witha stator of preferred size. The rotor had the same general dimensions asthat employed in Example 1 except for the restricted portion 45 at thebottom of the rotor. This restricted portion was 3/4" high, and openings47 and the corner radii were formed with a 0.75" end mill. Openings 47were 1.24" long, and 0.75" wide. The stator was 51/2" in outsidediameter, resulting in an outer edge overlapping the base of the slotsby 1/4".

In water model tests employing the special rotor, it was found that therotor could be operated at 600 RPM and a simulated gas flow of 5 CFM togive the same, very desirable smooth liquid surface previously obtainedonly at 3 CFM simulated gas flow and 450 RPM. The refining rateachievable in this embodiment, when operating at conditions of smoothsurface, was 100% greater than that obtainable using a conventionalrotor configuration in a refining chamber not equipped with the bafflemeans of the invention but operated at the conditions of smooth surfaceas indicated above.

The practice of the invention provides an advantageous advance in thealuminum refining art. The incorporation of the baffle means describedherein in the refining chamber serves to change the flow pattern ofmolten aluminum within the chamber so as to enable high gas flows and/ornozzle rotating speeds to be employed to achieve increased aluminumrefining rates without encountering the excessive surface turbulence ofthe molten aluminum that otherwise limits the desired increase in gasflows and nozzle rotating speeds. The baffle means of the invention isbelieved to reduce rotational flow along the bottom of the refiningchamber that otherwise inhibits desirable smooth upward flow of moltenaluminum into the rotor, and the achieving of a suitable and stablebalance of downward and upward molten aluminum flow into the rotor. Theembodiment of the invention in which the special rotor configurationdescribed above is employed has been found particularly advantageous,with the controlled upward flow of molten aluminum enabling particularlyenhanced gas flow rates and nozzle rotating speeds to be employedwithout undue surface turbulence.

It will be understood that various changes and modifications can be madein the details of the invention without departing from the scope of theinvention as set forth in the appended claims. Thus, while reference ismade herein to aluminum refining in general, the invention can bepracticed with respect to aluminum or to the various alloys thereof. Theinvention can be practiced in systems having refining chambers havingone or more refining compartments or stages, each of which is adaptedfor the positioning of a spinning nozzle assembly therein duringaluminum refining operations. In a typical two-stage refining system,molten aluminum is commonly passed into the inlet of the first stage andremoved from the outlet from the second stages. The separatecompartments are separated by a baffle adapted to enable molten aluminumto flow from the first stage to the second stage. Other such systems canincorporate more than two such refining stages therein. The bottombaffle means of the invention will desirably be employed in eachrefining compartment. Said baffle means can be constructed of anysuitable refractory material suitable for incorporation in the refiningchamber. Silicon carbide is a generally preferred material ofconstruction for this purpose, although other refractories, e.g.,graphite, can also be employed. While the baffle means is preferablypositioned so as to be located under the center of the rotor portion ofthe spinning nozzle assembly upon placement thereof in the refiningchamber, the baffle means may also be otherwise positioned so as to belocated under said rotor portion, but should not be positioned beyondthe periphery of the rotor.

The baffle means of the invention, as illustrated in FIGS. 6, 8 and 10of the drawings, are positioned at the floor of and extend all the wayacross the refining chamber. The baffle means serve to change the flowpattern of molten aluminum so as to enable higher gas flows and/ornozzle rotating speeds to be employed, without excessive surfaceturbulence. However, the presence of the thus-positioned baffle meansnecessarily makes it less convenient to carry out draining or cleaningoperations in the refining chamber. To facilitate such draining orcleaning operations while advantageously employing said baffle means,embodiments of the invention have been employed in which essentiallyopen space is provided at one or both ends of the baffle means at ornear the walls of the refining vessel. It enables the flow pattern to bechanged to enable higher gas flows and/or nozzle rotating speeds to beemployed, without excessive surface turbulence, while also facilitatingdraining and cleaning operations in the refining chamber operations inthe refining chamber. Thus, baffle means having the open spaces asprovided in this embodiment of the invention enables debris, such asthat formed in refining chamber cleaning operations, to be readilyscraped or pushed into one section of the bottom of the chamber forremoval.

In illustrative examples of the invention, a baffle arrangement as shownin FIG. 8 was employed, with baffle 25 having a baffle section 26 thatis 26" long and 4" high, with rotor 21 being positioned 2" above thebaffle, i.e., 6" above the floor of refining chamber 13. As shown inFIG. 13, holes 56 and 57 are cut out of baffle 25 at the lower portionof each end thereof near the side walls of the refining chamber.

The holes are 2" high and 4" wide, with the overall length of baffle 25being 26". The presence of such cut-outs was not found to affect therefining operation in any observable way. While holes of such size wereconvenient for purposes of the desired draining and cleaning operations,in which molten aluminum is removed from the refining chamber and inwhich debris is conveniently scraped or pushed into one portion of thebottom of the refining chamber for convenient removal, cut-out portionsof other suitable sizes can be employed for such purposes.

In further illustrative examples of the invention, straight baffles wereemployed without the end riser portions shown in FIG. 13. In theexamples, various baffle lengths were employed, with the baffle beingpositioned under the center of the rotor means used in refiningoperations. In addition to a full length baffle, shorter baffles, notextending all the way across the refining chamber from one side to theother, were employed. Thus, in FIG. 14, refining chamber 58 is shownwith spinning nozzle 59 having rotor 60 positioned therein, and withbaffle means 61 of shorter overall length than in the previouslyillustrated embodiments, positioned on the floor of the chamber. Openspaces 62 and 63 are thereby provided on each side of the chamber tofacilitate draining and cleaning operations. In each case, baffle means61 and rotor 60 were desirably centered in refining chamber 58, althoughthis is not essential for acceptable refining operation purposes.

Starting with a baffle 61 of full length, i.e., one extending all theway across the chamber from one end to the other, the baffle was firstshortened by cutting 2" from each end, making the baffle 22" long in arefining chamber 58 26" across. Thus, openings 62 and 63 were each 2"long from the wall of refining chamber 58 to the nearest end of baffle61. Using this shortened baffle, there was a small but noticeableincrease in surface roughness when the refining system, having theshortened baffle in place, was employed instead of the baffle extendingall the way across the refining chamber, which had the rotor of FIGS. 11and 12 positioned therein. The baffle means was then shortened inadditional increments of 4" down to a baffle 10" long, and then to abaffle 71/2" long, which is the same as the rotor diameter. Each step ofdecreased baffle length was found to decrease the effectiveness of thebaffle, upon use in refining operations. However, even the shortestbaffle was found to be advantageous as compared to the use of no baffleat all.

Those skilled in the art will appreciate that various changes andmodifications can be made in the details of this aspect of the inventionintended to facilitate draining and cleaning of the refining chamber,while achieving the beneficial effects of the baffle means in changingthe flow pattern of molten aluminum as described above. Baffles as shortas the rotor diameter are useful for purposes of the invention, i.e.,baffles having a length of about 30% of the width of the cheer, i.e.,the smallest horizontal dimension of the chamber. The particular lengthof the baffles useful in any given application will be determined by theoverall configuration and size of the refining chamber and the spinningnozzle employed.

While employing a shortened baffle providing open ends at both ends ofthe refining chamber, e.g., open ends 62 and 63 in FIG. 14, is generallydesired, it will be understood that the baffle means may also, in otherembodiments, extend from one side of the refining chamber in thedirection of the other side, such as to leave an open end at only oneside of the chamber, e.g., only open space 62 or 63, but not both.Likewise, the cut-out openings at the bottom of the baffle in thevicinity of the sides of the refining chamber, i.e., openings 56 and 57in FIG. 13, can be made of any convenient size for the desired drainingand cleaning purposes. If openings 56 and 57 in the FIG. 13 embodimentwere enlarged upward, it will be seen that such openings would approachthe open spaces 62 and 63 as provided by the shortened baffles of theFIG. 14 embodiment. It will also be understood that, in the practice ofthe cut-out opening embodiment of the invention, a cut out opening canbe provided at only one side of the refining chamber, desirably in thevicinity of the wall thereof, to provide the desired draining andcleaning capability, although the providing of openings at both ends ofthe baffle, preferably in the immediate vicinity of the side walls ofthe refining chamber is preferable.

It should be noted that, using the rotor as shown in FIG. 1 and 2 at arotor distance of 6" from the refining chamber floor, and employingbaffles extending all the way across the chamber and shortened baffles,down to 10" long, as in FIG. 14, the results were essentially the sameas when the rotor of FIGS. 11 and 12 were employed. At the shortestbaffle length, e.g., 71/2", it was necessary to adjust the position ofthe rotor downward, e.g., to 43/4" above the refining chamber floor, toobtain improved results by the use of the baffle means. At this rotorheight, the operation was further improved as the baffle length wasincreased in steps.

In other examples of the practice of this embodiment of the invention,the baffles were oriented in the refining chamber from one end to theother, i.e., for and aft, rather than being positioned along the shorterdistance across the chamber from one side to the other. In each case,the rotor of FIGS. 11 and 12 was employed at a rotor height of 6", usingstraight baffles of from 10" to 22" in length. In each case, the bafflesimproved performance, i.e., enabled a smoother surface of moltenaluminum to be obtained, but the amount of improvement was markedly lessthan when the baffle was oriented across the chamber in the preferredembodiments of the invention.

The invention will thus be seen, in enabling the maximum useful rate ofrefining in a refining chamber to be substantially increased overconventional practice, to provide a highly desirable and useful advancein the aluminum refining art.

I claim:
 1. In an insulated refractory lined refining chamber foraluminum refining, adapted for the positioning of a spinning nozzleassembly in a central region thereof for the injection of sparging gasinto molten aluminum present in the refining chamber during aluminumrefining operations, the improvement comprising vertical baffle meanspositioned at the floor of and extending across said refining chamber inthe portion of the floor under said central region of the refiningchamber, said baffle means being adapted to provide an open space in thevicinity of one or both side walls of the refining chamber to enablemolten aluminum to pass through during draining operations and to allowdebris to be scraped into one section of the floor of the refiningchamber for removal during cleaning operations, whereby said bafflemeans serves to change the flow pattern of molten aluminum within therefining chamber upon the use thereof for refining operations so as toenable higher gas flows and/or nozzle rotating speeds to be employedwithout excessive surface turbulence of said molten aluminum, whilefacilitating draining and cleaning operations in the refining chamber.2. The refining chamber of claim 1 in which said baffle means is such asto provide open spaces in the vicinity of each side wall of the refiningchamber.
 3. The refining chamber of claim 1 in which the baffle meanscontain one or more cut out openings to provide the open space in thevicinity of one or both side walls of the refining chamber.
 4. Therefining chamber of claim 3 in which said cut out openings are providedin the vicinity of each side wall of the refining chamber.
 5. Therefining chamber of claim 1 in which the length of the baffle means issuch that an open space is provided between the end of the baffle meansand the side wall of the refining chamber in the vicinity of one or bothside walls of the refining chamber, said baffle having a length of atleast about 30% of the length of a baffle extending all the way acrossthe floor of the refining chamber from one side to the other.
 6. Therefining chamber of claim 5 in which the baffle is positioned so as toprovide an open space in the vicinity of each side wall of the refiningchamber.
 7. The refining chamber of claim 4 in which said cut outopenings are positioned immediately adjacent to the side walls of therefining chamber.
 8. The refining chamber of claim 7 in which said cutout openings are on the order of 2" high and 4" long.
 9. The refiningchamber of claim 6 in which the distance across the refining chamber isabout 26", said baffle having a length of from about 22" to about 71/2".10. In an aluminum refining system adapted for the positioning of aspinning nozzle assembly in an insulated refractory lined refiningchamber for the injection of sparging gas into molten aluminum presentin the refining chamber during aluminum refining operations, theimprovement comprising a spinning nozzle assembly having a rotor portionpositioned in the insulated refractory lined refining chamber andvertical baffle means positioned at the floor of and extending acrosssaid refining chamber under the rotor portion of said spinning nozzleassembly, said baffle means being adapted to provide an open space inthe vicinity of one or both side walls of the refining chamber to enablemolten aluminum to pass through during draining operations and to allowdebris to be scraped into one section of the floor of the refiningchamber for removal during cleaning operations, whereby said bafflemeans serves to change the flow pattern of molten aluminum within therefining chamber upon the use thereof for refining operations so as toenable higher gas flows and/or nozzle rotating speeds to be employedwithout excessive surface turbulence of said molten aluminum, whilefacilitating draining and cleaning operations in the refining chamber.11. The refining chamber of claim 10 in which said baffle means ispositioned under the center of the rotor portion of said spinning nozzleassembly.
 12. The refining chamber of claim 10 in which the baffle meanscontain one or more cut out openings to provide the open space in thevicinity of one or both side walls of the refining chamber.
 13. Therefining chamber of claim 12 in which said cut out openings are providedin the vicinity of each side wall of the refining chamber.
 14. Therefining chamber of claim 10 in which the length of the baffle means issuch that an open space is provided between the end of the baffle meansand the side wall of the refining chamber in the vicinity of one or bothsaid side walls of the refining chamber.
 15. The refining chamber ofclaim 14 in which is positioned so as to provide an open space in thevicinity of each side wall of the refining chamber.